This invention relates to a bellows pump, which comprises a vertically disposed bellows and a pump head thereabove, the bellows being coupled to a motion conversion mechanism including an eccentric cam member driven by a motor for elongation and contraction along a vertical axis to effect pumping.
In a bellows pump, in a frame is provided a pump head having an inlet port and a discharge port, and also a conversion mechanism is provided, which operates to convert a rotational motion to a reciprocal motion and comprises, for instance, an eccentric cam member driven for rotation by a drive motor and a reciprocating member coupled to the excentric cam member. A bellows is vertically disposed between the pump head and conversion mechanism with an upper end section of the bellows mounted on a frame and communicated with the pump head and a lower end section of the bellows mounted in an upper connecting end portion of a reciprocating member coupled to the eccentric cam member constituting the motion conversion mechanism. With the operation of the motion conversion mechanism, the bellows is elongated and contracted to effect pumping.
In a well-known structure for mounting the bellows, the bellows is fixedly secured by a turn-buckle type mounting means, which is provided with a female thread member located at a communication hole of the pump head and screwed onto the upper end section of the bellows through a cap member and with an end cap member screwedly coupled to the lower end section of the bellows and the upper connecting portion of the reciprocating member.
In the above prior art bellows pump, the bellows is screwedly secured, and two separate parts, i.e., the cap member and end cap member, are required. Therefore, the operation of assembling the component parts requires an increased number of steps. Particularly, the operation of mounting the bellows in a limited narrow space presents problems in that it is not easy and takes considerable time.
Further, in the prior art bellows pump, the motor shaft support structure supports an eccentric cam member driven for rotation by the drive motor. In one of such well-known structures, the motor shaft of the drive motor is secured by set screws or the like to the eccentric cam member on one side thereof, and the cam member is driven for rotation by the sole motor, that is, the motor shaft is support for rotation in a bearing provided in a motor housing. In another structure, the motor shaft is fitted in and penetrates the eccentric cam member, and its free end projecting therefrom is supported for rotation on the frame on the other side of the eccentric cam member. In a further structure, not only a stem portion but also a free end portion of the motor shaft is supported for rotation on a frame.
The above prior art bellows pumps have problems. More specifically, where the eccentric cam member is supported for rotation by the sole motor, a load accompanying the elongation and contraction of the bellows in the vertical direction of elongation and contraction of the bellows perpendicular to the horizontal axial direction of the eccentric cam member, i.e., commonly called overhang load, is applied to the motor shaft via the eccentric cam member. This overhand load produces a stress in the entire motor shaft; particularly it produces a great stress in a portion of the motor shaft corresponding to a bearing provided in a motor housing.
Where the free end portion of the motor shaft is supported for rotation in a frame, the stress produced in the motor shaft due to overhand load is reduced compared to the above structure. This structure, however, is insufficient to solve the structure.
The structure in which not only the free end but also the stem of the motor shaft is supplied for rotation in a frame, can suppress stress in the portion of the motor shaft corresponding to the bearing provided in the motor housing. In this respect, it can solve the problem. In this case, however, the motor shaft has to be supported at two positions in the frame. This leads to an increase of the manufacturing cost. In addition, since the motor shaft should be long and penetrate the eccentric cam member, the operation of assembling the individual constituent parts is cumbersome.